A lightweight power propulsion attachment for manual wheelchairs will be developed to bridge the gap between manual and power wheelchairs for the majority the 2,500,000 users in the United States who depend entirely on wheelchairs for their mobility and quality of life. All manual wheelchair users encounter real-world situations that require strength and endurance that exceed their capabilities and are potentially detrimental to their health. When this occurs too frequently, users are forced to transition to power wheelchairs. While liberated from their physical limitations, power wheelchair users face significant disadvantages including high cost, total loss of therapeutic physical exertion and dramatically reduced transportability. Studies have found that maintaining mobility is essential for quality of life and reduces overall health care costs. Society as a whole also gains from users' full participation. It is therefore important to enable the user to extend as long as possible, without risking injury, the transition from manual to power wheelchairs. The proposed design replaces one front castor with a new castor coupled to an efficient and lightweight drive system steered with a manual joystick. The user can easily detach the entire drive unit and revert to the original manual wheelchair configuration. The lightweight power attachment unit can then be folded and stowed. The Phase II objectives are to complete the product development by adding the remaining required features, and optimizing the drive system, user interface, and structure. The specific aims are to meet weight, range, speed, traction, stability, reliability, cost, and ease of attaching/detaching requirements. These requirements were developed from user input, product analysis, and previous user, industry, and market studies. Phase II will begin with a detailed requirements analysis and design investigation. The design work will begin with the motor, gearbox, and brake systems. This will be followed by the design of the wheel coupling, the battery and power electronics, and the user interface. Complete industry standard tests will be performed at an established wheelchair test facility. User testing will verify functionality in real-world conditions. The combination of the simple, innovative design with the use of existing components, materials, and fabrication techniques results in a product with revolutionary features at a lower cost than existing products, creating an entirely new product category. With a superior market position, the power attachment is poised to capture a significant market share of the $800 million dollar power mobility industry. A successful introduction of this innovative product will stimulate further technical innovation in an industry constrained by antiquated structural and technological paradigms. A cost effective, exceptionally lightweight power propulsion attachment for manual wheelchairs will be developed that can be easily attached/detached by the user. This product will allow users to exercise their individual physical abilities without risking the injuries due to overexertion. The product seamlessly combines the transportability of manual wheelchairs with the functionality of power wheelchairs, increasing the overall mobility of the user. Studies have found that as mobility increases, quality of life is improved and health care costs are reduced.